By Irene D’Olivo, A.Celli Paper
Tissue papers are usually intended for the hygienic-sanitary market and, precisely for this reason, their most requested characteristics are softness and bulkiness. However, there are other important properties that depend, above all, on the type of fibres used and their processing.
In the production of tissue, we use short and long fibres: the former confer qualities such as softness and silkiness, while the latter reinforce and give strength to the structure of the web. The technological level of both the machinery and the process used for the production of Tissue papers also have a great impact on the final quality of the product. In short, with the right raw materials and chemical additives, combined with dedicated cutting-edge machinery, it is possible to produce a perfect tissue paper for top-of-the-range hygienic products.
So let’s see in detail what are the five main and essential properties that quality tissue must possess.
The bulkiness is defined as the volume occupied by a given weight of paper. This is an important property, as it is closely correlated with absorbency and softness, and is mainly determined by two factors: the production technologies and the quality of the fibres used.
To obtain a high bulkiness in the production phase it is possible to useadvanced technologiessuch as, for example, the Through-Air Drying process (or TAD), in which the wet pressing phase is reduced to minimum in favour of the drying operations that take place in the dryer section of the paper machine. In addition to production technology, other factors determining bulkiness are the use of lower pressure in the press nips, less intensive refining of the fibres and the creping of the paper.
As regards the type of fibres to be used, to obtain a high bulk it is recommended to prefer high-yield cellulose pulps, rigid and less subject to collapse thanks to the higher lignin content and lower porosity.
Absorbency is a fundamental property for any tissue product dedicated to drying liquids. The sheet must therefore have both a high absorption speed, in order to effectively carry out its drying action, and a high liquid-holding capacity, to remove as much liquid as possible. Absorbency is given by the type of fibre used, the refining operations, the creping performed, the layers present in the final product and the additives used.
The tissue paper sheet, in its life cycle, is subjected to significant stresses during production operations, in the converting phase and, finally, during use by the consumer. Hence the need to obtain a sheet with an adequate level of strength, given by the combination of three factors:
- strength and arrangement of fibres in the sheet;
- level of molecular bond between the fibres themselves;
- presence of strength additives.
Specifically, the first two factors depend on the process variables and the type of raw material used, while the use of additives is a widespread practice to add further strength to the fibres.
Some tissue products, such as kitchen paper, must be resistant even when wet, and this characteristic depends on the level of molecular bond between the fibres they are made of. In order to maintain the wet strength of these products as much as possible,additives can be used to supplement or replace the hydrogen bond of the fibres. In this way, it is possible to ensure that the Tissue paper maintains up to 50% of its dry strength when wet.
Softness, while still being a subjective measure based on individual perceptions, is a very important requirement and sought after by consumers, especially as regards products dedicated to the hygienic-sanitary or personal care markets. Furthermore, the perception of softness does not depend only on touch, but also on sound and visual perceptions such as colour (the degree of whiteness) and noise at the moment of tearing.
Softness is usually divided into surface softness, related to the velvet-like feeling to the touch, and bulk softness, which is an indication of the ease with which the paper yields when crumbled.
How to maintain the 5 properties of tissue at the end-of-line, thanks to A.Celli solutions
These five qualities, obtained during the production process of the paper sheet, must also be preserved in the subsequent phases, from the winding of the Jumbo rolls up to the shipment of the final reels to the converter. This is why A.Celli offers its customers a wide choice of winders, unwinders and rewinders of the E-WIND® range able to adapt to any production requirement in terms of speed, width and weight, with specific focus on bulky tissue paper characterized by high crepe ratios.